1. Field of the Invention
This invention relates generally to a rectifier bridge assembly such as for use in automotive alternators, and, more particularly, to an improved rectifier bridge assembly for dissipating heat.
2. Description of the Related Art
A rectifier bridge assembly, commonly called a rectifier, is one of the components parts of an alternator assembly forming a portion of the electrical charging system in an automobile. The basic role of the charging system is to replenish the charge of a battery with electricity generated by the alternator. The electrical current generated by the alternator is an alternating current (AC), while the electrical current preserved in the battery is a direct current (DC). The alternating current must be converted to a direct current so that the battery can be charged. This conversion is called rectification, and is the specific function of a rectifier bridge assembly.
The alternator used in a typical automobile is a three-phase type of alternating current (AC) electrical generator. The electricity generated by each phase must be rectified by one rectifier bridge. Each rectifier bridge consists of two diodes and, thus, three rectifier bridges are required for one alternator. Therefore, a typical rectifier bridge assembly consists of three rectifier bridges with six diodes. Three of the six diodes are connected to a ground, and the other three diodes are connected for DC output charging to the battery.
During the rectification process, tremendous amounts of heat are generated by converting the alternating current (AC) to direct current (DC). The heat must be dissipated as quickly and efficiently as possible, or the diodes may be ruined within a relatively short period of time. Therefore, the rectifier bridges are normally soldered onto heat sinks of good heat-conductive materials. Usually a portion of the ground provides a negative heat sink, and some structure associated with the DC output charging to battery provides a positive heat sink that is conductively and terminally isolated from the ground.
Rectifier bridges assemblies are normally assembled as an integrated part of an alternator assembly. The electrical current output of the alternator to the battery greatly depends on the capacity of the rectifier bridge assembly to rectify the alternating current to a direct current. However, the performance of the rectifier bridge assembly with the diodes at a set power level depends heavily on the heat disbursing ability of the heat sinks utilized. The faster heat can be disbursed from the rectifier bridge assembly, the cooler the rectifier can operate. The rectifier also has a longer life and a greater performance. Hence, the capability of the heat sink(s) should be a major concern in the design of a rectifier bridge assembly.
Traditionally rectifier bridges assemblies used in automobiles had two heat sinks, one for the negative side and the other for the positive side. This traditional heat sink design, however, was replaced by the demand to conserve space in an otherwise over-crowded engine compartment. For example, in the rectifier bridge assembly used on Ford Motor Company's 2G alternators, all six diodes are soldered in manner that disperses heat through only one heat sink within an area not greater than 3.6 square inches. This particular design, which is now common in the industry, tends to have a very poor heat dispersing capacity. The poor heat dispersing capacity of such rectifiers makes them fail more easily and prematurely.
One solution for improving the heat dissipating properties in a rectifier bridge assembly of the type such as found in the Ford 2G alternator is disclosed in U.S. Pat. No. 5,892,676 to Hsieh and which is incorporated herein by reference.
In light of the demand to decrease part size in the engine compartment, other attempts to limit the size of the rectifier bridge assembly have been attempted. One such solution has been attempted alternators found in vehicles manufactured by General Motors Company under the series designation “CS” which stands for Charging System manufactured by Delco Remy America, Anderson, Ind. and the series designation “AD” which stands for Air-cooled design with Dual internal fans manufactured by Delphi Corp., Troy, Mich. These designs like the Ford 2G alternator type use a single heat sink to disperse the heat; however, the positive and negative rectifier diodes are not arranged in series as with the Ford 2G type designs, but are arranged in parallel and separated in spaced apart relation throughout wells in the heat sink to reduce the overall thickness of the rectifier bridge assembly and to provide improved heat distribution throughout the heat sink. While fit for its intended purpose, the CS and AD series of alternators suffers from high heat due to the reduced effectiveness of the smaller heat sink. This among other issues has increased the failure rate of the rectifier bridge assembly in the CS and AD series of alternators and causes decreased performance as well. With reference to FIG. 1, Press-fit Diode, a diode assembly 20 for a CS type rectifier bridge assembly is shown in which the diode is formed from a semiconductor material called rectifier die 22 soldered between two copper tabs 24 and 26 and then embedded in epoxy 28 for insertion in one of the holes of the heat sink 29. A lead 30 extends out of the epoxy 28 from the upper copper tab 26 for connecting with the rectifier bridge circuit (not shown) and the opposite side, copper tab 24 is soldered to a metal cap 32, which is pressed fit for connecting in circuit to a positive or negative heat sink as appropriate. There are two drawbacks from this configuration, the first, the air gaps exist between the diode assembly and the heat sink created by the knurl on metal cap, and the second, only limited heat is dispersed through the narrow knurl ring on the metal cap to heat sink; this causes the effectiveness of the heat sink to be greatly reduced.
Accordingly, there has been a need for a novel rectifier bridge assembly that overcomes the above-noted problems in prior art designs. Such a novel rectifier bridge assembly must be adapted for use with standard alternator assemblies and have a design that may be manufactured cost effectively. The present invention fulfills these needs and provides other related advantages.